1. Technical Field
The present invention relates to a battery pack and a process for the production thereof.
2. Description of the Related Art
The related art battery pack is arranged such that an elementary battery cell is received in an outer case. The outer case insulates and protects the metal case of the cell. This battery pack is prepared by receiving an elementary battery cell in an outer case prepared by molding a plastic. This structure requires many producing steps that add to the production cost. In recent years, a production method has been developed which comprises inserting a cell in an outer case at a step of forming an outer case. This battery pack is disclosed in Patent Reference JP-A-2000-315483, the content of which is incorporated herein by reference. This battery pack is prepared by temporarily fixing a battery core pack having a holder and a cell connected to each other in a mold for forming a molded resin product which is an outer case, and then inserting and fixing the core pack in the outer case thus formed. In order to prepare this battery pack, it is not necessary that the core pack be received in a separately formed outer case during assembly. Therefore, this battery pack can be mass-produced efficiently.
However, this battery pack is disadvantageous in that the actual production thereof adds to production cost, it takes much time to accurately fix the battery core pack temporarily in the predetermined position and the production yield is reduced. The reason why the production cost rises is that a complicated mold allowing easy release of the outer case thus formed and a mechanism for driving this mold are required in addition to the necessity of accurately fixing the core pack temporarily in the predetermined position in such a manner that the core pack is not moved. Further, the reason why it takes much time to temporarily fix the core pack is that the core pack must be certainly attached to the open mold at a predetermined position. Moreover, the reason why the production yield is reduced is that the plastic to be molded into the outer case penetrates unnecessary portions under injection pressure or the molten plastic cannot be accurately injected into desired portions. Further, the method which comprises inserting the battery core pack partly in the mold at the step of forming the outer case to produce a battery pack is disadvantageous in that it is difficult to cover the surface of the cell by the outer case. In particular, it is extremely difficult to cover the surface of the cell by a thin outer case. This is because the thickness of the cell has an error that differs from position to position. For example, a thin battery cannot have a completely flat surface on the-both sides. For example, a thin battery which is bent such that it protrudes at the center thereof is thicker at the center thereof than at the edge thereof. When a molten plastic is then injected into the mold for forming the outer case for covering both sides of the battery with such a cell temporarily fixed in the forming chamber of the mold, the resulting outer case is thinner at the position corresponding to the thick portion of the thin battery or the surface of the thin battery is partly exposed to the exterior of the outer case, producing defectives. It may be thought likely that this trouble can be eliminated by forming a thicker outer case for covering both sides of the thin battery. However, it is actually not possible to form a thicker outer case. This is because the thicker the outer case is, the thicker is the entire battery pack. The production of thin batteries requires an extreme technique for raising the charge capacity while minimizing the external size. The cell thus produced should not be received in a thick outer case to form a battery pack having a large external size. Therefore, in the battery pack produced by inserting a battery core pack in an outer case, the thin battery is not insulated by the outer case on both sides thereof. A label is bonded to the both sides of the cell so that the cell is insulated. The bonding of such a label requires the cost of the label and the cost of bonding the label, adding to the production cost.
The invention has been worked out for the purpose of eliminating these disadvantages of the related art battery pack. An important object of the invention is to provide a battery pack which can be mass-produced efficiently in a high yield at a reduced cost using a simple producing apparatus and a process for the production thereof.
Another important object of the invention is to provide a battery pack which can be covered and insulated on both sides thereof by a thin plastic protective layer having a uniform thickness even if the external size of the cell has an error.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.